CN1208866C - Lithium secondary battery using nano surface coating composite material as positive electrode active material - Google Patents

Abstract

The present invention belongs to the technical field of high-energy batteries. The lithium secondary battery of the present invention is composed of a positive electrode with a nano-surface-coated modified composite material as an active material, a negative electrode with a material capable of storing lithium, an electrolyte solution, a polymer electrolyte or a solid electrolyte diaphragm, a current collector, a battery shell and a lead. The coating material used is one or more of semi-metals, oxides or salt substances, and its particle diameter is 0.1-200nm and the average thickness is 0.5-200nm. The lithium secondary battery of the present invention has high reversible capacity, good cyclability, safety and reliability, and is suitable for a variety of occasions. The present invention can be made into a variety of specifications such as button type and cylindrical.

Description

Lithium secondary battery with nano surface coated composite material as positive electrode active material

technical field

The invention belongs to the technical field of high-energy batteries, in particular to manufacturing lithium ion batteries and secondary lithium batteries.

Background technique

Currently, positive electrode active materials used in lithium-ion batteries mainly include LiCoO ₂ and LiNiO ₂ with a rock salt structure and LiMn ₂ O ₄ with a spinel structure. Among them, the theoretical specific capacity of LiCoO ₂ is 272 mAh/g, and the actual specific capacity is between 120-140 mAh/g. It is the earliest positive electrode active material used in commercial lithium-ion batteries. Due to its stable performance and easy synthesis, it is now widely used in commercial small-capacity lithium-ion batteries. However, due to the low reserves of Co, it is difficult to reduce the production cost of lithium-ion batteries using _LiCoO2 as the cathode material, which will become an important constraint factor for the production and promotion of large-capacity lithium-ion batteries. The theoretical specific capacity of LiNiO ₂ is similar to that of LiCoO ₂ , the actual available specific capacity is higher than that of LiCoO ₂ , and the production cost is lower than that of LiCoO ₂ . However, it is very difficult to synthesize single-phase LiNiO ₂ in the process, and the structure of LiNiO ₂ is not as stable as LiCoO ₂ , and there are safety hazards during overcharging, so it is difficult to popularize and use at present. Mn is abundant in nature, and the synthesis process of spinel LiMn ₂ O ₄ is simpler than that of LiNiO ₂ . Therefore, spinel LiMn ₂ O ₄ is the most promising application in the new generation of lithium-ion batteries, especially high-capacity lithium-ion batteries. Cathode materials in ion batteries. However, the theoretical specific capacity of LiMn ₂ O ₄ is only 148 mAh/g, and the highest available specific capacity is currently between 100-110 mAh/g. When the battery works at a higher temperature, the Mn ³⁺ in the Li _1-x Mn ₂ O ₄ in the charged state will dissolve into the acidic electrolyte containing a small amount of water, so LiMn ₂ O ₄ is used as the positive electrode active There are serious self-discharge phenomena and rapid reversible capacity decay in the battery of the material (Document 1, Electrolyte Effects on Spinel Dissolution and Cathodic Capacity Losses in 4 V Li/Li _x Mn ₂ O ₄ Rechargeable Cells; Dong H. Jang and Seung M. Oh; Journal of the Electrochemical Society 1997, Vol. 144, No. 10, p. 3342). In addition, due to the relatively complicated synthesis process, LiMnO ₂ with a rock-salt structure is still in the research stage of the laboratory, and there are no reports about its application in actual batteries.

By replacing Ni, Mn or Co with elements Mg, Al, Ti, Ga, Mn, W, the structural stability of LiNiO ₂ and LiMn ₂ O ₄ can be improved, the cycle performance of the material can be improved or the production cost of LiCoO ₂ can be reduced, but the element A shortcoming that substitution or doping brings is that the specific capacity (document 2, Synthesis and Characterization of New LiNi _1-y Mg _y O ₂ Positive Electrode Materials for Lithium Ion Batteries; C.Pouillerie, L.Croguennec, Ph. Biensan, P. Willmann and C. Delmas, Journal of the Electrochemical Society 2000 Vol. 147 No. 6 p. 2061).

In recent years, the research on cathode materials has a tendency to develop towards multi-ion transition metal salts, especially phosphates and pyrophosphates, such as LiFePO ₄ and LiFeP ₂ O ₇ , etc. The successful development of such cathode materials is expected to further Reduce the cost of cathode materials for lithium-ion batteries and promote the development and production of high-capacity batteries. However, an important shortcoming of this type of material is that the electrical conductivity is low, so it is not suitable for preparing lithium secondary batteries with high power density (document 3, Phospho-olivine as Positive-Electrode Materials for Rechargeable Lithium Batteries; AK Padhi, KSNanjundaswamy and JBGoodenough ; Journal of the Electrochemical Society, 1997, Vol. 144, No. 4, p. 1188).

Obviously, the existing positive electrode active materials cannot meet the requirements of producing lithium secondary batteries with large capacity or high power. To improve the actual specific capacity and cycle performance of cathode materials, it is necessary to develop new cathode materials or modify existing materials to improve the electrochemical performance of materials. For the reasons for the reduction of the capacity of lithium secondary batteries, it is generally believed that the factors related to the positive electrode material are: (1) at a higher charging potential, the electrolyte decomposes and consumes a part of lithium, which makes the specific capacity of the material and the cycle of the battery The performance is reduced; (2) at a higher state of charge, the active transition metal ions in the positive electrode material leave the material body and enter the electrolyte, reducing the active components in the positive electrode material; (3) in the case of a deep lithium deficiency in the positive electrode material state, the transition metal ions in the positive electrode material migrate and rearrange, and the crystal structure of the material undergoes an irreversible phase change, which reduces the electrochemical activity of the positive electrode material; (4) The trace amount of water contained in the currently used electrolyte makes the electrolyte acidic, Corrosive to alkaline cathode materials.

Contents of the invention

The purpose of the present invention is to change the local charge distribution state on the surface of the positive electrode material particles by surface coating treatment on the particles or electrode surface of the existing lithium secondary battery positive electrode material, thereby changing the surface physical and chemical properties of the positive electrode active material , so that the positive electrode active material can be charged to a higher potential, improve the specific capacity and specific energy of the positive electrode material, and at the same time ensure that the cycle performance of the material is not reduced, thereby increasing the energy density of the battery, improving the charge and discharge performance of the battery, and providing a battery with A lithium secondary battery with high charge and discharge capacity, good cycle performance and safety performance.

The purpose of the present invention is achieved like this:

The positive electrode material commonly used in lithium secondary batteries modified by nanometer surface coating is used as the positive electrode active material. The cladding material is semi-metal, oxide or salt substance, the particle diameter of which is between 0.1-200nm, and the average thickness is 0.5-200nm.

Compared with the material before coating, the physical and chemical properties of the surface of the coated positive electrode material have changed greatly: 1) The surface coating layer separates the active material in the inner layer from the electrolyte, which not only reduces the high potential. The capacity loss caused by electrolyte decomposition prevents the transfer of transition metal ions in the active material to the electrolyte. 2) Since the coating treatment occurs on the surface of the active material, the concentration of the ions of the surface coating material on the surface of the active material is much greater than the concentration change in the active material caused by doping, so the structure of the material can be more effectively stabilized, Inhibit the occurrence of irreversible phase transition and improve its cycle performance. 3) Coating such a thin layer of material on the surface of the active material will neither affect the transport properties of lithium ions inside the active material nor have a significant impact on the transport properties of the active material. On the contrary, due to the change of the surface properties of the active material by surface coating modification, the surface-treated positive electrode active material can be charged to a higher potential without causing electrolyte decomposition; and because the positive electrode active material can withstand higher charging Potential, the positive electrode active material after this treatment has higher specific capacity and specific energy. Therefore, it is ensured that the specific capacity of the material is increased without sacrificing the cyclability of the material, and the specific capacity and cyclability of the material are both improved at the same time.

The coating material of the present invention can be the mixture of one or more of the following types of materials:

(1) Semimetal: carbon material. Including various hard carbon materials, soft carbon materials, graphite, graphitized materials and modified graphite materials.

(2) Oxides: oxides or composite oxides formed from metals or nonmetals of groups IIA-VIIIA and IIB-VIB in the second to sixth periods of the periodic table of chemical elements. Specifically, Mg, Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Ga, Ge, Ba, Y, Zr, Mo, In, Sn, Ta, W, La, Pr , Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ce formed oxides or composite oxides, such as MgO, Al ₂ O ₃ , SiO ₂ , SnO, TiO ₂ , SnO ₂ , V ₂ O ₅ , MO ₂ , MnO ₂ , Fe ₂ O ₃ , Fe ₃ O ₄ , LiCr ₂ O ₄ , LiAlO ₂ , LiCoO _{2 , LiNiO 2 ,} LiMn ₂ O ₄ .

(3) Salts: Li ₃ PO ₄ , AlPO ₄ , Mg ₃ (PO ₄ ) ₂ , LiMPO ₄ (M=Mg, Fe, Co, Ni, Cr, Ti, or V) or LiF.

The coating treatment of active materials can choose one of the following methods according to different coating materials:

Method 1: Dissolving an appropriate amount of coating material precursor in an appropriate solvent, and then adding some surface pretreated active material powder into the above solution and stirring continuously to obtain a homogeneous mixture. The mixture was heated appropriately to remove solvent. The solvent-removed mixture is heated at an appropriate temperature and atmosphere to decompose the precursor of the coating material to obtain a nanometer surface-coated composite material positive electrode active material.

Method 2: Dissolve an appropriate amount of coating material precursor in an appropriate solvent and atomize and spray it into the reaction chamber, add the surface-pretreated active material powder to be coated into the reaction chamber and perform fluidization, and the fluidized The coating particles meet the atomized coating material precursor to form capsules. The capsules are collected and heated in an appropriate temperature and atmosphere to decompose the precursor of the coating material to obtain the positive electrode active material of the nanometer surface coating composite material.

Method 3: Grinding and mixing an appropriate amount of coating material precursor and active material powder to be coated in a ball mill, and then heating the mixture at an appropriate temperature and atmosphere to make the coating material precursor react to form a coating material , the positive electrode active material of the nanometer surface-coated composite material can be obtained.

Method 4: Dissolving an appropriate amount of certain precursor A of the coating material in an appropriate solvent, mixing and stirring with the powder of the active material to be coated to form a uniform mixture. Gradually add a solution of another precursor B of the coating material to the stirring mixture, control the pH value of the mixture, and make the precipitate formed by the reaction of the precursor A and B of the coating material coat the surface of the active material. After repeated washing and filtering, the obtained filtrate is heated at an appropriate temperature and atmosphere to obtain the positive electrode active material of the nanometer surface-coated composite material.

The basic structure of the lithium secondary battery of the present invention is: a positive electrode with a nano-surface coated modified composite material as the positive electrode active material, various materials that can store lithium as the negative electrode, an organic or inorganic electrolyte solution or a polymer electrolyte or a solid electrolyte It is composed of electrolyte, separator, current collector, battery case and lead. One end of the positive pole and the negative pole are respectively welded with lead wires and connected to the two ends of the mutually insulated battery case or the electrode post.

The lithium secondary battery of the present invention can be made into various forms and specifications such as button type (single layer), cylindrical shape (multilayer winding), square shape (multilayer folding) etc. from the above basic structure.

The lithium secondary battery of the present invention has high reversible capacity, good cycle performance, safety and reliability; it can be applied to various occasions, such as mobile phones, notebook computers, portable electronic devices, cordless electric tools and other mobile power supply occasions, as well as electric vehicles, Hybrid electric vehicles (including electric bicycles, electric motorcycles, electric tricycles) and other fields.

Description of drawings

FIG. 1 is a schematic structural diagram of an experimental lithium secondary battery of the present invention. Among them, 1 and 2 are mutually insulated battery shells, 3 and 4 are the spring pieces of the positive electrode and the negative electrode respectively, 5 and 6 are the supporting steel sheets of the positive electrode and the negative electrode respectively, 7 is the polytetrafluoroethylene screw, and 8 is the positive electrode current collector, 9 is a negative electrode current collector, 10 is a positive electrode material, 11 is a negative electrode material, and 12 is a diaphragm or a polymer electrolyte soaked in an electrolyte.

Figure 2 is the charge and discharge curves (2.5-4.3V) of the first and tenth weeks of the experimental battery using the nano-MgO surface-coated modified LiCoO ₂ composite material as the positive electrode.

Figure 3 is the charge and discharge curves (2.5-4.5V) of the first and tenth weeks of the experimental battery using the nano-MgO surface-coated modified LiCoO ₂ composite material as the positive electrode.

Fig. 4 is the charge-discharge curve (2.5-4.7V) of the first cycle and the tenth cycle of the experimental battery using the nano-MgO surface-coated modified LiCoO ₂ composite material as the positive electrode.

Fig. 5 is the charge and discharge curves (3.0-4.3V) of the first cycle and the tenth cycle of the experimental battery using the nano-Al ₂ O ₃ surface-coated modified LiCoO ₂ composite material as the positive electrode.

Fig. 6 is the charge-discharge curve (3.0-4.5V) of the first cycle and the tenth cycle of the experimental battery using the nano-Al ₂ O ₃ surface-coated modified LiCoO ₂ composite material as the positive electrode.

Fig. 7 is the charge-discharge curve (3.0-4.8V) of the first cycle and the tenth cycle of the experimental battery using the nano-Al ₂ O ₃ surface-coated modified LiCoO ₂ composite material as the positive electrode.

Fig. 8 is the charge-discharge curve (2.5-4.3V) of the first and tenth cycle of the experimental battery using the nano-SnO surface-coated modified LiCoO ₂ composite material as the positive electrode.

Fig. 9 is the charge-discharge curve (2.5-4.5V) of the first and tenth cycle of the experimental battery using the nano-SnO surface-coated modified LiCoO ₂ composite material as the positive electrode.

Figure 10 is the charge-discharge curves (3.0-4.5V) of the first cycle and the tenth cycle of the experimental battery using the nano- _SiO 2 surface-coated modified LiCoO ₂ composite material as the positive electrode.

Figure 11 is the charge-discharge curves (2.5-4.3V) of the first cycle and the tenth cycle of the experimental battery using the nano-LiMgPO ₄ surface-coated modified LiCoO ₂ composite material as the positive electrode.

Figure 12 is the charge-discharge curves (2.5-4.5V) of the first cycle and the tenth cycle of the experimental battery using the nano-LiMgPO ₄ surface-coated modified LiCoO ₂ composite material as the positive electrode.

Figure 13 is the charge-discharge curves (2.5-4.7V) of the first cycle and the tenth cycle of the experimental battery using the nano-LiMgPO ₄ surface-coated modified LiCoO ₂ composite material as the positive electrode.

Figure 14 is the charge-discharge curves (2.5-4.7V) of the first cycle and the tenth cycle of the experimental battery using the nano-LiFePO ₄ surface-coated modified LiCoO ₂ composite material as the positive electrode.

Figure 15 is the charge and discharge curves (2.5-4.3V) of the first and tenth cycles of the experimental battery using the nano-AlPO ₄ surface-coated modified LiCoO ₂ composite material as the positive electrode.

Figure 16 is the charge-discharge curves (2.5-4.5V) of the first and tenth cycles of the experimental battery with the nano-AlPO ₄ surface-coated modified LiCoO ₂ composite material as the positive electrode.

Figure 17 is the charge-discharge curves (2.5-4.7V) of the first and tenth cycles of the experimental battery using the nano-LiFePO ₄ surface-coated modified LiCoO ₂ composite material as the positive electrode.

Figure 18 is the charge-discharge curves (2.5-4.7V) of the first and tenth weeks of the experimental battery using the nano-C surface-coated modified LiCoO ₂ composite material as the positive electrode.

Figure 18 is the charge-discharge curves (2.5-4.5V) of the first and tenth weeks of the experimental battery using the nano-C surface-coated modified LiFePO ₄ composite material as the positive electrode.

Detailed ways

Example 1:

In order to illustrate the electrochemical performance of the lithium secondary battery of the present invention, an experimental battery was used as an example. Its structure is shown in Figure 1, and the battery is assembled in an argon-filled glove box with H ₂ O content below 1.0ppm. The electrolyte solution is 1M LiPF ₆ dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio is 1:1). The coating treatment of the positive electrode active material adopts the above-mentioned method 4. The cyclohexane solution of LiCoO ₂ (thickness of the coating layer is 10nm; LiCoO ₂ powder particle diameter is 5 μm), acetylene black and 5% PVDF (polyvinylidene fluoride) modified by nano-surface coating with MgO at room temperature Mixed under normal pressure to form a slurry, evenly coated on the aluminum foil substrate. The thickness of the obtained film is between 5-40 μm. After drying the obtained film at 150°C, press it under a pressure of 20Kg/cm ² , continue drying at 150°C for 12 hours, and then cut the film into a circular sheet with an area of 1 cm ² as the positive electrode sheet. The weight ratio of each part of the electrode material on the positive electrode sheet is 85:10:5. The preparation method of the negative electrode sheet is similar to that of the positive electrode sheet. The cyclohexane solution of natural graphite, acetylene black and polyvinylidene fluoride is mixed at normal temperature and pressure to form a composite slurry, which is evenly coated on the copper foil as the current collector. , the resulting film thickness is between 2-20 μm. Then make it dry at 150°C, compact it at a pressure of 20Kg/cm ² , and continue to dry at 150°C for 12 hours. The weight ratio of the dried negative electrode material (natural graphite), acetylene black and binder is about 85:10:5, and the obtained film is cut into discs with an area of 1 ^cm2 as the negative electrode sheet.

After drying all the battery materials except the electrolyte in Figure 1, the experimental battery was assembled as shown in Figure 1 in an argon-filled glove box. The experimental battery is subjected to a charge-discharge cycle test by an automatic charge-discharge instrument controlled by a computer. The current density is 0.2mA/cm ² , the charge cut-off voltage is 4.3, and the discharge cut-off voltage is 2.5V. The battery charge and discharge data are listed in Table 1.

In order to illustrate the charge and discharge characteristics of the composite positive electrode material modified by nanometer surface coating relative to lithium, the simulated battery assembled by the nanometer surface coated modified composite cathode material in the first week and the tenth week is listed in Figure 2. charge and discharge curve. The assembly and structure of the simulated battery are exactly the same as the aforementioned battery, except that the negative electrode is replaced by metal lithium foil. The current density of the charge-discharge cycle test is 0.2mA/cm ² , the charge cut-off voltage is 4.3V, and the discharge cut-off voltage is 2.5V.

Example 2

The LiCoO ₂ composite cathode material (the average thickness of the coating is 10nm, and the average particle diameter of LiCoO ₂ powder is 5 μm) with nano-MgO for surface coating modification (using method 4), acetylene black and 5% PVDF The cyclohexane solution is mixed at normal temperature and pressure to form a slurry, which is evenly coated on the aluminum foil substrate, and the thickness of the obtained film is about 5-40 μm. The remaining preparation steps of the positive electrode are the same as in Example 1.

The method for preparing the negative electrode is the same as in Example 1. The assembly of the simulated battery is the same as in Example 1. The current density of the charge-discharge cycle test is 0.2mA/cm ² , the charge cut-off voltage is 4.5V, and the discharge cut-off voltage is 2.5V. The charging and discharging curves are shown in Figure 3. The charging and discharging data are listed in Table 1.

Example 3

The LiCoO ₂ composite cathode material (the average thickness of the coating is 10nm, and the average particle diameter of LiCoO ₂ powder is 5 μm) with nano-MgO for surface coating modification (using method 4), acetylene black and 5% PVDF The cyclohexane solution is mixed at normal temperature and pressure to form a slurry, which is evenly coated on the aluminum foil substrate, and the thickness of the obtained film is 5-40 μm. The remaining preparation steps of the positive electrode are the same as in Example 1.

The method for preparing the negative electrode is the same as in Example 1. The assembly of the simulated battery is the same as in Example 1. The current density of the charge-discharge cycle test is 0.2mA/cm ² , the charge cut-off voltage is 4.7V, and the discharge cut-off voltage is 2.5V. The charging and discharging curves are shown in Figure 4. The charging and discharging data are listed in Table 1.

Example 4

The LiCoO ₂ composite cathode material (the average thickness of the coating is 5nm, _the average particle _size of LiCoO ₂ powder is 5 μm), acetylene black and 5 The cyclohexane solution of % PVDF is mixed at normal temperature and pressure to form a slurry, which is evenly coated on an aluminum foil substrate, and the thickness of the obtained film is about 5-40 μm. The remaining preparation steps of the positive electrode are the same as in Example 1.

The method for preparing the negative electrode is the same as in Example 1. The assembly of the simulated battery using polyacrylonitrile + LiClO ₄ + propylene carbonate + ethylene carbonate (20:5:45:30 weight ratio) polymer electrolyte is the same as in Example 1. The current density of the charge-discharge cycle test is 0.2mA/cm ² , the charge cut-off voltage is 4.3V, and the discharge cut-off voltage is 3.0V. The charging and discharging curves are shown in Figure 5. The charging and discharging data are listed in Table 1.

Example 5

Nano-Al ₂ O ₃ surface coating modification (using method 4) LiCoO ₂ composite cathode material (the average thickness of the coating is 2nm, the average particle size of LiCoO ₂ powder is 5 μm), acetylene black and 5% PVDF The cyclohexane solution is mixed at normal temperature and pressure to form a slurry, which is evenly coated on the aluminum foil substrate, and the thickness of the obtained film is about 5-40 μm. The remaining preparation steps of the positive electrode are the same as in Example 1.

The method for preparing the negative electrode is the same as in Example 1. Polyacrylonitrile + LiClO ₄ + propylene carbonate + ethylene carbonate (20:5:45:30 weight ratio) polymer electrolyte was used. The assembly of the simulated battery is the same as in Example 1. The current density of the charge-discharge cycle test is 0.2mA/cm ² , the charge cut-off voltage is 4.5V, and the cut-off voltage is 3.0V. The charging and discharging curves are shown in Figure 6. The charging and discharging data are listed in Table 1.

Example 6

Nano Al ₂ O ₃ surface coating modification (method 4) LiCoO ₂ composite positive electrode material (the average thickness of the coating is 0.5nm, the average particle size of LiCoO ₂ powder is 5μm), acetylene black and 5% PVDF The cyclohexane solution is mixed at normal temperature and pressure to form a slurry, which is evenly coated on the aluminum foil substrate, and the thickness of the obtained film is about 5-40 μm. The remaining preparation steps of the positive electrode are the same as

Example 1.

The method for preparing the negative electrode is the same as in Example 1. Polyacrylonitrile + LiClO ₄ + propylene carbonate + ethylene carbonate (20:5:45:30 weight ratio) polymer electrolyte was used. The assembly of the simulated battery is the same as in Example 1. The current density of the charge-discharge cycle test is 0.2mA/cm ² , the charge cut-off voltage is 4.8V, and the discharge cut-off voltage is 3.0V. The charging and discharging curves are shown in Figure 7. The charging and discharging data are listed in Table 1.

Example 7

Nano-SnO surface coating modification (using method 3) LiCoO ₂ composite cathode material (the average thickness of the coating is 50nm, the average particle size of LiCoO ₂ powder is 5 μm), acetylene black and 5% PVDF cyclohexane The solution is mixed at normal temperature and pressure to form a slurry, which is evenly coated on an aluminum foil substrate, and the thickness of the obtained film is about 5-40 μm. The remaining preparation steps of the positive electrode are the same as in Example 1.

The method for preparing the negative electrode is the same as in Example 1. The assembly of the simulated battery is the same as in Example 1. The current density of the electric cycle test is 0.2mA/cm ² , the charge cut-off voltage is 4.3V, and the discharge cut-off voltage is 2.5V. The charging and discharging curves are shown in Figure 8. The charging and discharging data are listed in Table 1.

Example 8

Nano-SnO surface coating modification (using method 3) LiCoO ₂ composite cathode material (the average thickness of the coating is 50nm, the average particle size of LiCoO ₂ powder is 5 μm), acetylene black and 5% PVDF cyclohexane The solution is mixed at normal temperature and pressure to form a slurry, which is evenly coated on an aluminum foil substrate, and the thickness of the obtained film is about 5-40 μm. The remaining preparation steps of the positive electrode are the same as in Example 1.

The method for preparing the negative electrode is the same as in Example 1. The assembly of the simulated battery is the same as in Example 1. The current density of the electric cycle test is 0.2mA/cm ² , the charge cut-off voltage is 4.5V, and the discharge cut-off voltage is 2.5V. The charging and discharging curves are shown in Figure 9. The charging and discharging data are listed in Table 1.

Example 9

Nano- _SiO2 surface coating modification (using method 2) _LiCoO2 composite cathode material (the average thickness of the coating is 5nm, the average particle size of _LiCoO2 powder is 5μm), acetylene black and 5% PVDF cyclohexene The alkane solution is mixed at normal temperature and pressure to form a slurry, which is evenly coated on the aluminum foil substrate, and the thickness of the obtained film is about 5-40 μm. The remaining preparation steps of the positive electrode are the same as in Example 1.

The method for preparing the negative electrode is the same as in Example 1. The assembly of the simulated battery is the same as in Example 1. The current density of the charge-discharge cycle test is 0.2mA/cm ² , the charge cut-off voltage is 4.5V, and the discharge cut-off voltage is 3.0V. The charging and discharging curves are shown in Figure 10. The charging and discharging data are listed in Table 1.

Example 10

Nano-LiMgPO ₄ surface coating modification (using method 4) LiCoO ₂ composite cathode material (the average thickness of the coating is 20nm, the average particle size of LiCoO ₂ powder is 5 μm), acetylene black and 5% PVDF cyclohexene The alkane solution is mixed at normal temperature and pressure to form a slurry, which is evenly coated on the aluminum foil substrate, and the thickness of the obtained film is about 5-40 μm. The remaining preparation steps of the positive electrode are the same as in Example 1.

The method for preparing the negative electrode is the same as in Example 1. The assembly of the simulated battery is the same as in Example 1. The current density of the charge-discharge cycle test is 0.2mA/cm ² , the charge cut-off voltage is 4.3V, and the discharge cut-off voltage is 2.5V. The charging and discharging curves are shown in Figure 11. The charging and discharging data are listed in Table 1.

Example 11

The LiCoO ₂ composite positive electrode material (the average thickness of the coating is 30nm, _the average particle size of the LiCoO ₂ powder is 5 μm), the acetylene black and 5% PVDF The cyclohexane solution is mixed at normal temperature and pressure to form a slurry, which is evenly coated on the aluminum foil substrate, and the thickness of the obtained film is about 5-40 μm. The remaining preparation steps of the positive electrode are the same as in Example 1.

The method for preparing the negative electrode is the same as in Example 1. The assembly of the simulated battery is the same as in Example 1. The current density of the charge-discharge cycle test is 0.2mA/cm ² , the charge cut-off voltage is 4.5V for discharge, and the discharge cut-off voltage is 2.5V. The charging and discharging curves are shown in Figure 12. The charging and discharging data are listed in Table 1.

Example 12

The LiCoO ₂ composite positive electrode material (the average thickness of the coating is 10nm, the average particle size of the LiCoO ₂ powder is 5 μm) with nanometer LiMgPO ₄ for surface coating modification (using method 4), acetylene black and 5% PVDF The cyclohexane solution is mixed at normal temperature and pressure to form a slurry, which is evenly coated on the aluminum foil substrate, and the thickness of the obtained film is about 5-40 μm. The remaining preparation steps of the positive electrode are the same as in Example 1.

The method for preparing the negative electrode is the same as in Example 1. The charging and discharging data are listed in Table 1. The assembly of the simulated battery is the same as in Example 1. The current density of the charge-discharge cycle test is 0.2mA/cm ² , the charge cut-off voltage is 4.7V, and the discharge cut-off voltage is 2.5V. The charging and discharging curves are shown in Figure 13.

Example 13

LiCoO ₂ composite positive electrode material (the average thickness of the coating is 40nm, and the average particle size of LiCoO ₂ powder is 5 μm) coated with nanometer LiFePO ₄ surface modified (using method 4), acetylene black and 5% PVDF cyclohexene The alkane solution is mixed at normal temperature and pressure to form a slurry, which is evenly coated on the aluminum foil substrate, and the thickness of the obtained film is about 5-40 μm. The remaining preparation steps of the positive electrode are the same as in Example 1.

The method for preparing the negative electrode is the same as in Example 1. The assembly of the simulated battery is the same as in Example 1. The current density of the charge-discharge cycle test is 0.2mA/cm ² , the charge cut-off voltage is 4.7V, and the discharge cut-off voltage is 2.5V. The charging and discharging curves are shown in Figure 14. The charging and discharging data are listed in Table 1.

Example 14

Nano-AlPO ₄ surface coating modification (using method 4) LiCoO ₂ composite cathode material (the average thickness of the coating is 2nm, the average particle size of LiCoO ₂ powder is 5 μm), acetylene black and 5% PVDF cyclohexene The alkane solution is mixed at normal temperature and pressure to form a slurry, which is evenly coated on the aluminum foil substrate, and the thickness of the obtained film is about 5-40 μm. The remaining preparation steps of the positive electrode are the same as in Example 1.

The method for preparing the negative electrode is the same as in Example 1. The assembly of the simulated battery is the same as in Example 1. The current density of the charge-discharge cycle test is 0.2mA/cm ² , the charge cut-off voltage is 4.3V, and the discharge cut-off voltage is 2.5V. The charging and discharging curves are shown in Figure 15. The charging and discharging data are listed in Table 1.

Example 15

Nano-AlPO ₄ surface coating modification (using method 4) LiCoO ₂ composite positive electrode material (the average thickness of the coating is 1nm, the average particle size of LiCoO ₂ powder is 5 μm), acetylene black and 5% PVDF cyclohexene The alkane solution is mixed at normal temperature and pressure to form a slurry, which is evenly coated on the aluminum foil substrate, and the thickness of the obtained film is about 5-40 μm. The remaining preparation steps of the positive electrode are the same as

Example 1.

The method for preparing the negative electrode is the same as in Example 1. The assembly of the simulated battery is the same as in Example 1. The current density of the charge-discharge cycle test is 0.2mA/cm ² , the charge cut-off voltage is 4.5V, and the discharge cut-off voltage is 2.5V. The charging and discharging curves are shown in Figure 16. The charging and discharging data are listed in Table 1.

Example 16

LiCoO ₂ composite positive electrode material (the average thickness of the coating is 10nm, and the average particle size of LiCoO ₂ powder is 5 μm) coated with nano-LiFePO ₄ surface modified (using method 4), acetylene black and 5% PVDF cyclohexene The alkane solution is mixed at normal temperature and pressure to form a slurry, which is evenly coated on the aluminum foil substrate, and the thickness of the obtained film is about 5-40 μm. The remaining preparation steps of the positive electrode are the same as in Example 1.

The method for preparing the negative electrode is the same as in Example 1. The assembly of the simulated battery is the same as in Example 1. The current density of the charge-discharge cycle test is 0.2mA/cm ² , the charge cut-off voltage is 4.7V, and the discharge cut-off voltage is 2.5V. The charging and discharging curves are shown in Figure 17. The charging and discharging data are listed in Table 1.

Example 17

Nano-C surface coating modification (using method 1) LiCoO ₂ composite cathode material (the average thickness of the coating is 50nm, the average particle size of LiCoO ₂ powder is 5 μm), acetylene black and 5% PVDF cyclohexane The solution is mixed at normal temperature and pressure to form a slurry, which is evenly coated on an aluminum foil substrate, and the thickness of the obtained film is about 5-40 μm. The remaining preparation steps of the positive electrode are the same as in Example 1.

The method for preparing the negative electrode is the same as in Example 1. The assembly of the simulated battery is the same as in Example 1. The current density of the charge-discharge cycle test is 0.2mA/cm ² , the charge cut-off voltage is 4.7V, and the discharge cut-off voltage is 2.5V. The charging and discharging curves are shown in Figure 18. The charging and discharging data are listed in Table 1.

Example 18

Nano-C surface coating modification (using method 2) LiFPO ₄ composite cathode material (the average thickness of the coating is 100nm, the average particle size of LiCoO ₂ powder is 5 μm), acetylene black and 5% PVDF cyclohexane The solution is mixed at normal temperature and pressure to form a slurry, which is evenly coated on an aluminum foil substrate, and the thickness of the obtained film is about 5-40 μm. The remaining preparation steps of the positive electrode are the same as in Example 1.

The method for preparing the negative electrode is the same as in Example 1. The assembly of the simulated battery is the same as in Example 1. The current density of the charge-discharge cycle test is 0.2mA/cm ² , the charge cut-off voltage is 4.7V, and the discharge cut-off voltage is 2.5V. The charging and discharging curves are shown in Figure 19. The charging and discharging data are listed in Table 1.

Table 1. The charge and discharge data table of the experimental battery using the surface-coated modified composite material as the positive electrode active material Covering material active material Charging voltage discharge voltage Initial discharge specific capacity loop parameter MgO _LiCoO2 4.5 2.5 182 0.033 MgO _LiCoO2 4.7 2.5 207 0.019 Al ₂ O _{3 LiCoO2} 4.3 3.0 135 0.052 Al ₂ O _{3 LiCoO2} 4.5 3.0 192 0.001 Al ₂ O _{3 LiCoO2} 4.8 3.0 207 0.034 SnO _LiCoO2 4.3 2.5 151 0.060 SnO _LiCoO2 4.5 2.5 183 0.005 SnO _LiCoO2 4.7 2.5 205 0.078 SiO _{2 LiCoO2} 4.5 3.0 188 0.112 LiPO _{4 LiCoO2} 4.3 2.5 145 0.025 LiPO _{4 LiCoO2} 4.5 2.5 178 0.031 LiPO _{4 LiCoO2} 4.7 2.5 204 0.051 LiMgPO _{4 LiCoO2} 4.3 2.5 138 0.029 LiMgPO _{4 LiCoO2} 4.5 2.5 170 0.006 LiMgPO _{4 LiCoO2} 4.7 2.5 198 0.061 LiFePO _{4 LiCoO2} 4.5 2.5 163 0.012 AlPO _{4 LiCoO2} 4.3 2.5 148 0.054 AlPO _{4 LiCoO2} 4.5 2.5 164 0.030 AlPO _{4 LiCoO2} 4.7 2.5 210 0.103 C _LiCoO2 4.3 2.5 162 0.013 MgO _LiNiO2 4.3 2.5 176 0.053 MgO _LiNiO2 4.5 2.5 224 0.106 Al ₂ O _{3 LiNiO2} 4.3 2.5 177 0.057 Al ₂ O _{3 LiNiO2} 4.5 2.5 232 0.114 SnO _LiNiO2 4.5 2.5 221 0.089 LiMgPO _{4 LiNiO2} 4.5 2.5 228 0.093 C _LiNiO2 4.3 2.5 183 0.021 MgO LiNi _0.8 Co _0.2 O ₂ 4.3 2.5 166 0.025 MgO LiNi _0.8 Co _0.2 O ₂ 4.5 2.5 206 0.036 Al ₂ O ₃ LiNi _0.8 Co _0.2 O ₂ 4.3 2.5 178 0.043 Al ₂ O ₃ LiNi _0.8 Co _0.2 O ₂ 4.5 2.5 212 0.063 SnO LiNi _0.8 Co _0.2 O ₂ 4.5 2.5 218 0.072 LiMgPO ₄ LiNi _0.8 Co _0.2 O ₂ 4.5 2.5 220 0.092 C LiNi _0.8 Co _0.2 O ₂ 4.5 2.5 215 0.039 AlPO ₄ LiNi _0.8 Co _0.2 O ₂ 4.5 2.5 222 0.106 Li ₃ PO ₄ LiNi _0.8 Co _0.2 O ₂ 4.5 2.5 228 0.096 MgO LiMn ₂ O ₄ 4.5 2.5 127 0.023 ^* Al ₂ O ₃ LiMn ₂ O ₄ 4.5 2.5 131 0.016 ^* SnO LiMn ₂ O ₄ 4.5 2.5 124 0.011 ^* LiMgPO ₄ LiMn ₂ O ₄ 4.5 2.5 128 0.013 ^* C LiMn ₂ O ₄ 4.5 2.5 130 0.025 ^* AlPO ₄ LiMn ₂ O ₄ 4.5 2.5 123 0.010 ^* Li ₃ PO ₄ LiMn ₂ O ₄ 4.5 2.5 129 0.026 ^* C LiFePO ₄ 4.0 2.5 125 0.011 TiO _{2 LiNiO2} 4.5 2.5 195 0.135 _{SnO2 LiNiO2} 4.5 2.5 187 0.126 V ₂ O _{5 LiNiO2} 4.5 2.5 192 0.113 _{MnO2 LiCoO2} 4.5 2.5 168 0.057 _{Fe2O3 _} LiMn ₂ O ₄ 4.5 2.5 132 0.063 ^* _{LiCr2O4 _} LiMn ₂ O ₄ 4.5 2.5 135 0.059 ^* _{LiAlO2 LiCoO2} 4.5 2.5 166 0.025 _LiCoO2 LiMn ₂ O ₄ 4.5 2.5 138 0.116 ^* _LiNiO2 LiMn ₂ O ₄ 4.5 2.5 135 0.125 ^* LiMn ₂ O _{4 LiCoO2} 4.5 2.5 178 0.035 Mg ₃ (PO ₄ ) ₂ LiMn ₂ O ₄ 4.5 2.5 137 0.104 ^* _LiCoPO4 LiMn ₂ O ₄ 4.5 2.5 133 0.095 ^* _{LiNiPO4 LiCoO2} 4.5 2.5 175 0.024 LiVPO _{4 LiCoO2} 4.5 2.5 173 0.037 _{LiTiPO4 LiCoO2} 4.5 2.5 169 0.025 LiF LiMn ₂ O ₄ 4.5 2.5 136 0.103 ^*

Note: 1) The initial specific capacity value is calculated based on the positive electrode active material (including the coating material), that is, the actual first-week discharge capacity divided by the mass of the positive electrode active material. The cycle parameter refers to the difference between the discharge specific capacity of the first week minus the discharge specific capacity of the 10th week, divided by the discharge specific capacity of the first week;

2) The unit of voltage is "volt"; the unit of capacity is "mAh/g";

3) The measurement temperature is generally 25-30°C; the measurement temperature of those marked with ^* is 55°C.

Claims (5)

1. Lithium secondary battery with nano-surface coated composite material as positive electrode active material, including negative electrode for lithium storage, organic or inorganic electrolyte, and separator between positive and negative electrodes soaked in electrolyte solution or polymer electrolyte or solid electrolyte open, sealed into the battery case, and the wires drawn from the positive and negative electrodes are respectively connected to the battery case or electrode column insulated from each other. The active material is LiNi _x Co( _1-x) O ₂ 0≤x≤1 or LiMn ₂ O ₄ or LiFePO ₄ ; the coating material is semi-metal, oxide or salt, which is one or more coating materials The average thickness of the coating layer is 0.5-200nm, and the particle diameter is 0.1-200nm; the composite slurry formed by mixing the nano-surface coating modified composite material with the binder and the conductive agent is evenly coated or rolled on the conductive surface. A thin film is made on the carrier. After the thin film is dried, it undergoes densification treatment, then dried, and then cut into the desired shape according to the battery specifications. 2. The lithium secondary battery using the nano-surface coated composite material as the positive electrode active material according to claim 1, wherein the semi-metal is a carbon material. 3. The lithium secondary battery with the nano surface coating composite material as the positive electrode active material according to claim 1, characterized in that: the oxide is composed of IIA in the second to sixth periods of the periodic table of chemical elements - Oxides or composite oxides formed of metals and nonmetals of Group VIIIA and IIB-VIB. 4. According to claim 1, the lithium secondary battery with the nano-surface coated composite material as the positive electrode active material is characterized in that: the oxide is composed of Mg, Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Ga, Ge, Ba, Y, Zr, Mo, In, Sn, Ta, W, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Oxide or compound oxide formed by Er, Tm, Yb, Lu, Ce. 5. The lithium secondary battery using the nano-surface coating composite material as the positive electrode active material according to claim 1, characterized in that: the salts are Li ₃ PO ₄ , AlPO ₄ , Mg ₃ (PO ₄ ) ₂ , LiF, LiMPO ₄ where M is Mg, Fe, Co, Ni, Cr, Ti or V.

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